In general, in an image forming apparatus such as a laser printer, a cartridge containing toner is detachably attached to a main body of the apparatus. For example, JP-A-2006-267994 discloses an image forming apparatus capable of determining whether the attached cartridge is a new product (new product detection) and also determining type of the cartridge (type detection).
Specifically, an image forming apparatus disclosed in JP-A-2006-267994 includes an arm-shaped swayable actuator, a spring for urging the actuator to a neutral position, a sensor for detecting a swing of of the actuator, and a controller the new product detection and the type detection based on a signal from the sensor, all of which are provided in a main body of the apparatus. A cartridge attached to the image forming apparatus includes: one or two contact projections that extend radially outward from a predetermined shaft portion; a detection gear that rotates integrally with the contact projection(s) around the shaft portion; and a gear mechanism that meshes with the detection gear and that transmits driving force to a stirring plate (agitator) in the cartridge.
In the image forming apparatus, when the cartridge is attached to the main body of the apparatus, the contact projection(s) presses one end of the actuator thereby the actuator swings. The sensor detects the swing of the actuator. A signal detected by the sensor is transmitted as a first detection signal to the controller. Upon receipt of the first detection signal, the controller determines the cartridge is a new product.
In the image forming apparatus, when, for example, a front cover is closed after attachment of a cartridge, the controller performs warm-up operation (idle rotation operation). The term “idle rotation operation” means an operation to rotate the agitator in order to agitate toner contained in the cartridge.
In such idle rotation operation, a transmission force from a drive source provided in the main body of the apparatus is transmitted to the agitator and the detection gear in the cartridge by way of the gear mechanism. As a result, the agitator starts agitation of toner, and the contact projection(s) rotates to further push the one end of the actuator. Thereby, the contact projection(s) is separated from the actuator at a predetermined position. Subsequently, the actuator returns to a neutral position by means of urging force of the spring. At this time, when two contact projections are provided, the second contact projection presses the one end of the actuator again to allow the actuator to swing. The swing of the actuator is detected by the sensor. A signal detected by the sensor is transmitted as a second detection signal to the controller.
Upon receipt of the second detection signal, the controller determines the type of the cartridge to be type A (e.g., a type where the maximum sheets to be printed are 6000). When the second detection signal is not received, the controller determines the type of the cartridge to be type B differing from type A (i.e., a type in which the maximum sheets to be printed are 3000).
When the detection gear rotates by a predetermined amount after the second contact projection has swayed the actuator, the detection gear is disengaged from a gear mechanism and does not rotate. Thereby, when a used cartridge is temporarily removed and again attached to the main body of the apparatus, the actuator does not swing by the contact projection, and hence the controller determines that the cartridge is an old product on condition that the detection signal is not transmitted at all.
With reference to FIGS. 8 and 9, an example detection gear will be described. As shown in FIG. 8, a detection gear CG has contact projections TB and a gear tooth portion GT is provided in only a portion of an outer periphery of the gear, whereby a remaining portion of the gear becomes a toothless portion NT. Thus, as shown in FIG. 9, the detection gear CG is configured such that, when the gear tooth portion GT is disengaged from the gear mechanism (only one transmission gear TG is illustrated), the gear does not rotate any further.
As shown in FIG. 8, an elastically-deformable rib R is formed in the detection gear CG so as to extend in an axial direction, and a V-shaped projecting portion B that deforms the rib R in a radially internal direction is formed in a case C that supports the detection gear CG shown in FIG. 9. As shown in FIGS. 9A to 9C, the rib R gradually becomes deformed toward radially inward direction during a movement from a base end of the V-shaped projection portion B to an apex thereof. After crossing the apex, the rib R gradually restores its original shape by means of restoration force. In the structure shown in FIG. 9, the detection gear CG independently rotates by utilization of the restoration force of the rib R acting on an inclined surface of the projection portion B. As a result, when the rib R crosses the apex of the projecting portion B, the transmission gear TG is disengaged from the gear tooth portion GT. Thus, the detection gear CG independently rotates by means of restoration force of the rib R after crossing the apex, whereupon the gear tooth portion GT departs from the transmission gear TG. As a result, the gear tooth portion GT and the transmission gear TG are prevented from again engaging with each other.
However, in the detection gear CG, the rib R may be deformed in a radially inward direction at the apex of the projection B as well as being deformed in a direction opposite to the rotating direction of the detection gear CG as a result that the rib R is caught by the apex. In this case, the rib R does not reach the inclined surface of the projection B (i.e., a inclined surface of the detection gear CG provided on a downstream side in the rotating direction), and hence a portion of the gear tooth portion GT of the detection gear CG remains meshed with the transmission gear TG. In a case where a portion of the gear tooth portion GT and the transmission gear TG remain meshed with each other, when the image forming apparatus is subsequently operated normally, flipping sound generates at an area where the transmission gear TG and the detection gear CG mesh with each other.